The present invention relates to the field of flow control in wide-area networks.
Data communications networks often employ a technique referred to as “flow control” to manage the transmission of data among network nodes. Generally, “flow control” refers to techniques for making the transmission of data from one node to another conditional upon some real-time criteria, such as whether there is sufficient buffer space at a receiver to receive a transmission, or whether the transmitter is complying with a specified transmission rate. There are different types of flow control mechanisms or protocols. On network links employing the Gigabit Ethernet data communications protocol, for example, a mechanism using Pause and Resume messages is utilized. When a receiver senses that receive buffers are close to full, it sends a Pause message to the transmitter indicating that the transmitter should stop transmission for a specified time. Later, when the buffers have become emptier, the receiver sends a Resume message indicating that transmission can be resumed. This Pause/Resume protocol keeps the risk of buffer overrun and loss of data at an acceptably low level.
Data communications networks often have a hybrid nature, such that an end-to-end data communications path traverses links or subnetworks that employ different transmission protocols. At the interfaces between subnetworks of different types, devices that perform encapsulation, protocol mapping, and related functions are used to enable the successful transfer of data from one subnetwork to another. The different subnetworks may use different flow control protocols, or in some cases a subnetwork using a flow control protocol may be connected to another subnetwork that does not. One configuration is the interconnection of two or more relatively local links, such as Gigabit Ethernet (GbE) links, via a more wide-area network, such as a Synchronous Optical Network (SONET) long-haul network. In such a configuration, the wide-area network (WAN) serves as a transport medium for the traffic of the local links, i.e., it functions much as a wire that simply moves data from one GbE link to another without participating in the GbE protocols. SONET, for example, has no provision for flow control, either internally or in relation to external network segments such as GbE links.
It may be desirable in networks having local-area segments interconnected by a WAN to employ flow control within the WAN in addition to whatever flow control is used on the local segments. However, for some WANs, such as SONET-based WANs, there may be no specification of a flow-control protocol, nor any anticipation of a need for flow control. Additionally, it may be desirable that protocol-mapping network devices used at the edges of a WAN be operable with different types of attached local networks, so that it may be necessary to support different flow control protocols or different methods for enabling subnetworks using different flow control protocols to interoperate with each other. Therefore, there is a need for mechanisms that can be flexibly utilized for flow control in a wide-area network and protocol-mapping devices attached thereto.